The invention relates to a pressing apparatus with a pressure plate for the hot pressing of materials from the group of the laminates, wood materials, wood/plastic materials, chip and flake boards, and wood, paper, film and pulp board combinations for floors, walls and ceilings, the pressing apparatus having at least one heated press platen, and wherein at least one resilient lining is arranged between the platen and the pressure plate.
In heated pressing apparatus of this kind, which may be parts of a single or multiple platen press, in order to achieve short cycling times and uniform pressing action the important thing is to provide for the greatest and most uniform heat transfer and an extremely uniform distribution of high pressing forces over the entire material. At the same time it must be remembered that the dimensions of the material may be 6 m×9 m and more.
Negative examples of poor heat transfer are double glazing for windows and Thermos vacuum vessels.
In the field to which the state of the art and the invention belong, the industry distinguishes between press pads and coated press plates.
Press Pads:
DE 26 27 442 A1 discloses a press pad for hot plate pressing, in which a cloth made of random fiber fleece is coated on both sides with silicone rubber.
EP 0 920 982 A1 discloses a press pad made from a fabric of crossed threads is disclosed, the core of which is, for example, a thread of a silicone elastomer with a Shore A hardness of 60 to 75 which is wrapped by at least one metal wire. The metal wires can be electrical heating resistances. But air inclusions between the fabric and the material being pressed are not excluded.
EP 1 040 909 A1 discloses providing an inherently resilient press pad with outer layers on both sides, which are joined together by a plurality of spacing threads. To improve heat transfer, at least some of the spacing threads consist of metal wires. However, these fall far short of compensating for the insulating action of the enclosed air cushion.
DE 200 11 432 U1 discloses, in the case of a press pad, the embedding of a textile fabric of polyamide and metal threads in a continuous layer of a polymer material resistant to heat and pressure.
It is furthermore disclosed by DE 100 34 374 A1, for the manufacture of a thermally conductive press pad with a maximum thickness of 2.2 mm and without air inclusions, to coat a metal fabric on both sides from the upper side with a silicone mass containing metal powder with a crosslinking agent, and to cure this press pad.
DE 200 13 422 U1 discloses a press pad of intersecting threads or bundles of threads, of which at least a portion have magnetic properties for fixation to a heating plate. Nothing is said about any elimination of insulating air inclusions.
A press pad is disclosed by DE 201 15 945 U1 in which thermally conductive filaments are partially embedded in a mass of rubber-resilient material and protrude from both outer sides of the press pad. In that case the air masses between the protruding metal filaments and the thermal conductivity of the metal filaments are diametrically opposed. Even if in the course of the very limited time of operation the metal filaments become incorporated into the resilient material, another problem arises, namely the inability of air trapped between the press lining and the platen to escape.
To enable the press to be opened, such short-lived press pads must be suspended from the platen, so that they sag down in the middle like hammocks, even if they do not contain magnetic material—as in the case, for example, of the subject matter of DE 200 13 422 U1—and even if the platen also consists of a magnetic material such as steel. Thus, however, the problem again increases that air inclusions between the press pads and the platen cannot escape at all or only slowly, and this problem increases with increasing smoothness of the surface which the platen is facing. In other words, here again the necessary hot contact and the air inclusions are diametrically opposed.
Coated Pressure Plates:
In practice, pressure plates are the plain metal sheets or metal plates, which consequently can also be called carrier plates because they have a carrying function for applied linings and linings of one or more components.
DE 39 11 958 A1 has disclosed a pressure plate for the cold pressing of mineral materials, in which at least one external layer of an ultra-high molecular weight thermoplastic, such as polyethylene, is applied to a light-metal plate as a pressure plate. Such a lining is hard. In this case, however, thermal transfer plays no part in the pressing of the material, the resilientity likewise plays no part in the leveling out of irregularities in the surface of the material being pressed.
DE 40 05 157 C1 has disclosed a pressure plate for the hot pressing of materials, for the production of very smooth surfaces on the material being pressed, wherein a corrosion-resistant and scratch resistant glass lining, which likewise is non-resilient in itself, is applied to the pressure plate. In this case again, the resilientity plays no part in the equalization of irregularities in the surface of the material being pressed.
In DE 42 09 670 C1, pressure plates are disclosed for a hot press for a material (decorative laminae with a textured surface) with a maximum thickness of 1.2 mm, wherein padding layers are arranged between the pressure plates and the platens. However, no information is given on their properties, particularly not about what materials the padding layers are made of, and whether they are free of air inclusions. The solution of a different problem is involved, namely the use of removable masks to shield surface areas not used in the pressing process against damage and contamination.
It is therefore the purpose of the invention to offer a coated pressure plate of the kind described in the beginning for hot presses, whereby brief cycle times and uniform and full surface press actions are achieved by the avoidance of air inclusions and cold spots, as well as an extremely uniform distribution of high pressing forces across the entire material, and long useful life and low product rejects are achieved, especially in the case of raw material dimensions of up to 6 m×9 m and over.
The solution of the stated problem is achieved by the invention, in the case of the pressure plate referred to in the beginning, by the fact that
a) the pressure plate has on the side facing the platen at least one lining of a thermally conductive, resilient plastic firmly adhering to the pressure plate, and that
b) the lining of the pressure plate is in contact free of air gaps with the platen.
With these features the stated problem is solved to the full extent. Short cycle times and uniform, full-surface press actions are achieved by avoiding air inclusions and cold spots, and with an extremely uniform distribution of high pressing forces over the entire material, with long production runs and few product rejects. This is especially true for raw material dimensions up to 6 m×9 m and over. Any increase in the usual working temperature of the platen of, for example about 200° C. can be prevented by avoiding air inclusions, thereby also preventing unnecessary heat losses.
As a result of further embodiments of the invention it is especially advantageous if, either singly or in combination:                the resilient lining has a Shore-A hardness between 40 and 80, especially between 50 and 70, and preferably of about 60,        the resilient lining consists of a silicone material,        the resilient lining is bonded to the pressure plate by an adhesive,        the resilient lining is provided with metal embedments in particle form,        the resilient lining has a thickness of 1 to 4 mm,        the resilient lining is divided into areas of different Shore A hardness,        the resilient lining has the relatively greatest Shore-A hardness at the marginal areas of the pressure plate,        the pressure plate has a thickness between 2 and 8 mm, preferably between 3 and 5 mm,        the pressure plate consists of at least one metal from the group: stainless steel, copper and brass,        the resilient lining of the pressure plate on the side facing the platen is provided with a layer of a soft metal,        the metallic layer consists of sheet copper and has a thickness between 0.3 and 0.4 mm,        the metallic layer consists of a fine metal mesh embedded in the resilient lining,        on the side facing the platen the pressure plate has an alternating series of layers of at least two resilient layers and at least two layers of soft metal from the group of the metal foils and metal meshes,        the overall structure of the coated pressure plate and of the platen is free of air inclusions,        the overall structure of the coated pressure plate is made at least largely self-supporting,        the overall structure of the coated pressure plate is fastened by at least one screw penetrating the pressure plate on the bottom of the platen, and/or, if        the overall structure of the coated pressure plate is fastened to the circumferential edge of the platen.        
The application of the resilient lining can be performed either by uniform brushing, extrusion from a slit nozzle, or it can be done by pouring an initially free-flowing composition from one or more nozzles in a predetermined very narrow and uniform distribution pattern onto the pressure plate, in which case the initially free-flowing composition spreads out at least largely by itself, and then the composition can be let stand until it reaches the predetermined Shore-A hardness; silicone resins are especially well suited for this purpose.